is there any javascript code that I can use to edit (and maybe download and later upload the modified) text file on a linux server?
So I do not have to leave my web browser and do ssh all the time when I need to edit or even only check some config files? The server is not accessible from the Internet.
You can use AJAX to read the file, then use more AJAX to call a server-side script that writes to the file, preferably without introducing a security hole.